In the production of X-rays for use in dental radiography, a stream of electrons is generated at a cathode by heating a tungsten filament. A stream of these electrons is caused to impinge at high velocity upon a tungsten anode from which is deflected a stream of X-rays. The movement of the electron stream at high velocity requires (1) the maintenance of the electron path under high vacuum and (2) the maintenance of high voltage differences between the cathode and anode. The housing for the X-ray generator must therefore be sealed and be well insulated from the high voltages. Usually the X-ray tube is supported in a sealed tank and surrounded with oil having a high dielectric constant.
The X-rays are focused on the patient's dental arch. In order to prevent escape of X-rays, the tube is secured within an X-ray opaque shield and the rays permitted to pass through a small opening provided in the shield. Centering this tube-shield and sealing the X-ray generator is critical if the X-rays are to be properly focused. Prior to the present invention, the centering operation has been accomplished by trial and error means and is time-consuming.